<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .wrap {
            width: 800px;
            height: 400px;
            position: relative;
        }
 
        .list {
            width: 800px;
            height: 400px;
            position: relative;
            padding-left: 0px;
        }
 
        .item {
            width: 100%;
            height: 100%;
            list-style: none;
            position: absolute;
            left: 0;
            opacity: 0;
            transition: all .8s;
        }
 
        .item:nth-child(1) {
            background-color: skyblue;
        }
 
        .item:nth-child(2) {
            background-color: yellowgreen;
        }
 
        .item:nth-child(3) {
            background-color: rebeccapurple;
        }
 
        .item:nth-child(4) {
            background-color: pink;
        }
 
        .item:nth-child(5) {
            background-color: orange;
        }
 
        .item.active {
            z-index: 10;
            opacity: 1;
        }
 
        .btn {
            width: 60px;
            height: 100px;
            z-index: 100;
            top: 150px;
            position: absolute;
        }
 
        #leftBtn {
            left: 0px;
        }
 
        #rightBtn {
            right: 0px;
        }
 
        .pointList {
            list-style: none;
            padding-left: 0px;
            position: absolute;
            right: 20px;
            bottom: 20px;
            z-index: 200;
        }
 
        .point {
            width: 10px;
            height: 10px;
            background-color: antiquewhite;
            border-radius: 100%;
            float: left;
            margin-right: 8px;
            border-style: solid;
            border-width: 2px;
            border-color: slategray;
            cursor: pointer;  
        }
 
        .point.active{
            background-color: cadetblue;
        }
    </style>
</head>
<body>
    <div class="wrap">
        <ul class="list">
            <li class="item active">0</li>
            <li class="item">1</li>
            <li class="item">2</li>
            <li class="item">3</li>
            <li class="item">4</li>
        </ul>
        <ul class="pointList">
            <li class="point active" data-index = 0></li>
            <li class="point" data-index = 1></li>
            <li class="point" data-index = 2></li>
            <li class="point" data-index = 3></li>
            <li class="point" data-index = 4></li>
        </ul>
        <!-- 左右交互按钮 -->
        <button class="btn"  id="leftBtn"> < </button> 
        <button class="btn" id="rightBtn"> > </button>
 
    </div>
</body>
<script>
    var items = document.querySelectorAll(".item");//图片节点
    var points = document.querySelectorAll(".point")//点
    var left = document.getElementById("leftBtn");
    var right = document.getElementById("rightBtn");
    var all = document.querySelector(".wrap")
    var index = 0;//全局变量
    var time = 0;//定时器跳转参数初始化
    

    //封装一个清除active方法
    var clearActive = function () {
        for (i = 0; i < items.length; i++) {
            items[i].className = 'item';
        }
        for (j = 0; j < points.length; j++) {
            points[j].className = 'point';
        }
    }

    //改变active方法
    var goIndex = function () {
        clearActive();
        items[index].className = 'item active';
        points[index].className = 'point active'
    }
    //左按钮事件
    var goLeft = function () {
        if (index == 0) {
            index = 4;
        } else {
            index--;
        }
        goIndex();
    }

    //右按钮事件
    var goRight = function () {
        if (index < 4) {
            index++;
        } else {
            index = 0;
        }
        goIndex();
    }
    

    //绑定点击事件监听
    left.addEventListener('click', function () {
        goLeft();
        time = 0;//计时器跳转清零
    })

    right.addEventListener('click', function () {
        goRight();
        time = 0;//计时器跳转清零
    })

    for(i = 0;i < points.length;i++){
        points[i].addEventListener('click',function(){
            var pointIndex = this.getAttribute('data-index')
            index = pointIndex;
            goIndex();
            time = 0;//计时器跳转清零
        })
    }
    //计时器轮播效果
    var timer;
    function play(){
     timer = setInterval(() => {
        time ++;
        if(time == 20 ){
            goRight();//向右轮播
            time = 0;
        }    
    },100)
}
    play();
    //移入清除计时器
    all.onmousemove = function(){
        clearInterval(timer)
    }
   //移出启动计时器
    all.onmouseleave = function(){
        play();
    }
</script>
</html>